Marine organisms such as algae, mollusks, tubeworms and barnacles attach to the surfaces of structures submerged in seawater, oceans, rivers and lakes. This marine growth on these surfaces may affect the integrity of the structure (e.g., ships, boats, pilings, water intake and outfall pipes) and can seriously hamper the operation of these systems. For example, on ship hulls the attachment of marine growth adversely affects the speed of the ship and its fuel efficiency due to the increased drag caused by the marine growth. For water intakes, there is an attendant loss of cooling efficiency in power generation and manufacturing process operation when such intakes have significant marine growth attached.
It has been common practice to coat the substrate surfaces of wood, plastic and metal with coating compositions that inhibit attachment and/or growth of marine organisms. Such coating compositions are usually referred to as antifoulant coatings or antifoulant paints and generally consist of a binder material, an antifouling agent (biocides and “booster biocides”), diluents and additives to aid in adhesion, flow, color, viscosity, stability, etc.
There is a concern for the possible effects of antifoulant compounds on the environment. One approach is the development and use of systems which attempt to control fouling through surface modification; for example, preventing attachment of algae and barnacles through the use of silicon or fluorine containing polymers having non-stick or release properties. Another approach is to use antifouling compounds that are toxic enough to marine life so that marine structures are not significantly fouled, but have a toxicity such that generally marine life is not harmed nor irreversibly altered. In this context, it is preferred that the compounds used as antifouling agents do not build up in the environment and cause deformation or adverse changes in marine life. It is desirable, for example, to provide antifouling agents that are less toxic than tributyltin (TBT) that has been used as an antifouling agent for many years and is now officially banned in some waters due to the harm to marine life that resulted from TBT leaching into the waters. In addition, TBT has caused deformations in oysters to develop thick shells and sex-changing disorders in whelks among other biological changes noted from its use.
Accordingly, a need exists for a wider variety of environmentally safe and effective antifouling marine coating compositions.